Vehicle safety and efficiency are concerns for any vehicle operator. Safety is important for the operator of a vehicle, for the passengers in the vehicle, and for others that share the road with the vehicle. Safe vehicle operation also may reduce vehicle repair costs and downtime. Efficiency also is important for the vehicle operator and the vehicle owner. Efficient vehicle operation may reduce operating and maintenance costs associated with a vehicle, thereby improving profit margins for a business that operates vehicles or possibly saving on maintenance, fuel, and administrative costs. Components that contribute to both vehicle safety and efficiency include axle components and drive train components. Axle components include wheels, wheel hubs, pneumatic tires, suspension components, braking components, and the like. Drive train components include a vehicle engine and components that transfer power from the engine to the drive wheels of the vehicle.
Proper maintenance of the vehicle is important to safe and efficient operation of the vehicle. Proper maintenance includes proper lubricant fluid levels, proper replacement of fluids, proper tire pressures, and the like. In the case of a pneumatic tire, for example, improper air pressure in the tire can lead to an increased likelihood of a failure of the tire due to increased heating and/or increased or uneven tread wear. Improper air pressure also can increase costs associated with operating the vehicle due to reduced life of the tire, thereby increasing replacement costs, and also increased rolling friction, thereby reducing fuel economy.
Accordingly, one important aspect of operating any vehicle is the proper maintenance of the vehicle. Proper maintenance facilitates optimal vehicle performance. In the case of an entity that operates a number of different vehicles, such as a trucking company, a rental car company, a delivery company, maintenance of fleet vehicles is particularly important. Proper maintenance helps ensure that costs associated with vehicle operation are not unnecessarily increased. However, maintenance has its own associated cost. The costs of proper maintenance include vehicle “downtime.” However, operating schedules of the entity may inhibit properly maintaining the vehicles. In other words, the volume of maintenance checks and the time required to perform such checks may result in vehicle maintenance being performed less often than is ideal as the vehicle is committed to jobs and tasks. Moreover, too much maintenance is an unwarranted expense.
The value of maintenance checks to confirm proper vehicle conditions offset some of the benefits of properly maintaining vehicles due to the costs associated with performing such checks as well as the vehicle downtime. Furthermore, when a vehicle is on the road, access to a suitable maintenance facility may be limited.
Various systems have been designed and are the subject of numerous patents that accomplish the objective of maintaining tire pressure within an acceptable range. These systems are typically called central tire inflation systems (CTIS). The most common systems in the heavy truck industry are designed for trailers. Trailer axles are typically hollow with axle ends that commonly have a through bore. The hollow axle provides a conduit to supply air pressure to the wheel end. The wheel end assembly includes a lubrication area between the axle and the wheel further defined by plugging the through bore in the axle end and covering the end of the axle with a hub cap attached to the wheel. The wheel is supported on the axle end by wheel bearings. The bearings require lubrication and the integrity of the lubrication area is essential in maintaining the operability and life of the wheel end assembly. In order to provide pressurized air to the rotating tires, the CTIS typically includes a rotary union assembly in the same general location as the bearings. The rotary union assembly is in or adjacent to the lubrication area between the stationary axle and the wheel.
Many tire inflation systems also provide an indication that air is flowing to one or more tires. Conventionally, CTIS provide a “go/no-go” or “flow/no-flow” indication that air is flowing through the system. These systems generally include a rubber diaphragm contained within the air flow conduit or hose. The diaphragm is provided with a bore to allow air to pass across the diaphragm to pressurize the system. As air travels in the system, the diaphragm moves in response to the air flow. The movement of the diaphragm in response to air flow closes an electrical circuit. The closed electrical circuit provides power to an indicator, such as a light, that indicates air is flowing through the system somewhere. Such a conventional system is described in U.S. Pat. No. 8,201,575, issued Jun. 19, 2012, titled Air Pressure Regulator with Flow Sensor, the disclosure of which is incorporated herein as if set out in full.
The indication may alert an operator or driver that there is a leak in one or more tires, or perhaps a leak in the tire inflation system. In any event, the presence of such a leak is an indication that the vehicle should be serviced to correct the problem. Traditional systems commonly rely on very simplistic flow switches, as described in the aforementioned U.S. Pat. No. 8,201,575, that use a differential pressure to close a mechanical switch. Traditionally, these systems require a wiring harness from the sensor to the indicator light, which adds to the installation costs. Conventionally, the only information provided is whether air is flowing. That air is flowing is typically provided by a light being illuminated in the nose of the trailer that a driver must identify via the rearview mirror. A driver must notice the illumination of a light behind the tractor cab on the nose of the trailer to even be alerted that a problem exists in the system. Also, the system only warns when flow exists, but it does not provide an indication of which wheel, which is problematic on larger vehicles, nor does it provide information regarding whether the flow relates to regular variations in tire pressure or is indicative of a problem or failure.
Another type of flow sensor for a CTIS is disclosed by U.S. Pat. No. 7,201,066, issued Apr. 10, 2007, titled System for Automatic Tire Inflation, the disclosure of which is incorporated herein as if set out in full. The '066 patent provides another mechanical sensor for gas flow to inflate the downstream tires. The '066 patent measures a pressure drop across a porous media element where there is a linear relationship between the pressure drop across the media and the flow rate of the gas through the meter.
As can be appreciated, conventional systems employ mechanical systems to measure pressure and/or differential pressure to determine whether flow exists in a system. These systems provide crude accuracy at best. Because of the crude measuring, most conventional CTIS provide an indication of flow only when air flow in the CTIS exceeds about 1.2 cubic feet per minute, which is essentially indicative of a tire blowout or a tube breakage.
The above and other mechanical system to indicate flow of air in the CTIS leave much to be desired. Thus, against this background it would be desirous to provide an indication to the vehicle operator of the actual flow rate of air through the system. Moreover, it would be desirous to provide information relating to which of the plurality of tire the air is flowing. Additionally, it would be desirous to provide a system that also provides a warning as well as an alarm to a vehicle operator based on various parameters associated with the CTIS. Finally, it would be desirous to provide a system that provides an indication of flow prior to a catastrophic failure, such as a blowout.